Method of and means for operating synchronous dynamo-electric machines.



W. J. FOSTER. METHOD OF AND MEANS FOR OPERATING SYNCHRONOUS DYNAMOELECTRIC MACHINES. APPLiICATION FILED AUG-30. 1913.

1,160,705, Patented Nov. 16, 1915.

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UNITED STATES PATENT OFFICE.

WILLIAM J. FOSTER, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

METHOD OF AND MEANS FOR OPERATING SYNCHRONOUS DYNAMO-ELECTRIC MACHINES.I

To all whom it may concern Be it known that I, WILLIAM J. Fos'rnn, acitizen of the United States, residing at -Schenectady, county ofSchenectady, State namo electric machines, and particularly to theoperation of such machines during the starting period.

It is well known that a synchronous motor or a rotary converter willhave a high starting torque with a minimum current input when it isstarted as an induction motor, but such a machine will have a largeslip, and unless the load thereon is small it will not pull intosynchronism. 4

My invention has for its object a novel method of and means foroperating such a dynamo electric machine, or any synchronous machine, sothat its speed will approach more nearly to that of synchronism thanwould be the case if it were started as a simple induction motor. Tothis end, I start the machine by supplying alternating current to itsalternating current winding so that it will start as an alternatingcurrent induction motor. The machine may have a short-circuitedsecondary winding or may be provided with poles of solid steel. In thelatter case the machine will operate substantially the same as if itwere provided with a short-circuited secondary winding.

I preferably provide the machine with a short-circuited secondarywinding in addition to a direct current exciting winding. After themachine has started as an induction motor I short circuit the directcurrent exciting winding of the machine on a resistance, which bringsthe speed of the machine closer to synchronism with a high torque andwith a comparatively small current input. The source of direct currentis then connected to the direct current exciting winding and the machinepulls into synchronism. I preferably connect the source of directcurrent to the direct current exciting Winding and the resistance whichshort-circuits this exciting winding in parallel without opening thecircuit of Specification of Letters Patent.

Patented Nov. 16, 1915.

Application filed August 30, 1913. Serial No. 787,485.

the direct current exciting winding, whereby the transition frominduction motor operation to synchronous motor operation is made withminimum line disturbance, due to the fact that there is no danger of themotor dropping in speed during the transition.

For a better understanding of my invention reference may be had to thefollowing description taken in connection with the accompanying drawing,in which the single. figure shows diagrammatically one embodiment of myinvention.

Referring to the drawing, 1 is an alternating current winding of asynchronous dynamo electric machine which is arranged to be connected toalternating current mains 2 in any well known manner. Any well knownform of compensator may be used, or a switch 3 may be used for thispurpose.

4 is a short-circuited secondary winding which may be of comparativelyhigh resistance, and -5 a direct current exciting winding, both of whichare on the field member, which I have shown as being the rotary memberof the machine. A resistance 6 is provided on which the direct currentexciting winding is short-circuited during the starting operation aswillhereinafter appear. Direct current mains 7 are provided forsupplying current to the exciting winding 5. A control switch 8 is shownfor making these connections.

The machine is started by supplying al-. ternating current to thewinding 1 of'the machine, whereupon it will operate as an inductionmotor with the short-circuited winding 4 performing the function of asecondary. When the motor reaches the maximum speed that it can as aninduction mo-- rangement of controller contacts shown in runningposition C, in which the resistance is. disconnected and the directcurrent mains are connected to the exciting winding only. The provisionof the transition position B on the controller permits the change frominduction motor operation to synchronous motor operation to be madewithout'opening the circuit of the winding 5. With this arrangement ofthe controller, there is no danger of the machine dropping in speedduring the transition and there will be therefore no disturbance on thelines 2.

I desire it to be understood that my invention is not limitedto theparticular arrangement shown and described, and aim in the appendedclaims to cover all modifications which do not depart from the spiritand scope of my invention. I i

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is

1. The method of operating a synchronous dynamo electric machineprovided with an alternating current winding on one member and a directcurrent exciting winding on its field member, which consists insupplying alternating current to its alternating current winding tostart the machine as an alternating current motor having. ashortcircuited secondary winding, then short-circuiting its directcurrent exciting winding on a resistance to supply the machine with asecond short-circuited winding, and then supplying direct current to theexciting .a second short-circuit ed winding, then supplying directcurrent to the exciting winding and the resistance inparallel to pullthe machine into synchronism, and then disconnecting the resistance.

a 3. In combination, a synchronous dynamo electric machine having amember provided with a short-circuited winding and a direct currentexciting winding, a source of direct current, a resistance, and meansfor closing said exciting winding on said resistance and for connectingsaid source to said exciting winding and the resistance in parallel.

4. In combination, a synchronous dynamo electric machine having a memberprovided with a short-circuited winding and a direct current excitingwinding, a source of direct current, a resistance, and means for closingsaid exciting winding on said resistance, for connecting said source tosaid exciting winding and said resistance in parallel, and fordisconnecting said resistance.

In witness whereof, I have hereunto set my hand this 29th day of August,1913.

WILLIAM J. FOSTER.

Witnesses BENJAMIN B. HULL, MARGARET E. WOOLLEY.

